This invention relates to a rail vehicle of the type for moving along a pair of parallel rails and including a plurality of pairs of wheels with each wheel of each pair arranged to engage a respective one of the rails and particularly to an apparatus in such a vehicle for detecting the distance between the vehicle and an remote obstacle on the rail.
In much of Canada and similar large countries there are many miles of rail track which is of the conventional simple double rail with no accompanying electrical wires or the like. In many cases also the rail is of a single track, that is traffic in both directions uses the same track with occasional double track portions for allowing passing. In such circumstances it is particularly important to ensure that the rail vehicles are properly spaced and that there is no possibility of such vehicles approaching one another in opposite directions on the same length of track.
Such techniques are normally carried out by separate control systems which monitor the position of trains on the track and which provide necessary signalling alongside the track to inform the engineer whether he is allowed to move forward along the track.
However, there remains a need, to supplement existing systems in case of failure, for a more direct indication within the vehicle as to whether there are obstacles on the track and particularly other vehicles or trains and the distance from those vehicles.
A number of proposals have been made for determining and controlling the distance between such rail vehicles but in most cases these require additional complex equipment separate from the vehicle on the track. In some cases the track or an adjacent conductor carries transmitted signals which are communicated to the vehicle and assist in determining the position of the vehicle relative to other such vehicles.
U.S. Pat. No. 4,133,505 (Bongiorno) discloses an arrangement in which each vehicle has a device for generating a current which is applied by a pantagraph to an overhead wire. The current is then withdrawn from the wire by the next adjacent vehicle so that the magnitude of the current is dependent upon the resistance of the overhead wire and thus the length of wire between each vehicle and the next.
However this device has a number of significant disadvantages. Firstly it requires a separate additional wire to be installed along the track. Secondly it requires a number of diodes along the wire to prevent current generated by a third vehicle from interfering with the proper measurement. Thirdly it requires each vehicle on the track to be equipped with the device. Fourthly it is incapable of detecting any obstacles other than another similarly equipped vehicle.
The above patented device therefore has apparently received little or no success and certainly has not been adopted in Canada where the large lengths of track already existing without the additional necessary wires effectively prevent the economic acceptance of such a device.
It is one object of the present invention, therefore, to provide an apparatus for detecting the distance between the vehicle and a remote obstacle which does not require the addition of further trackside equipment and merely requires the positioning of a suitable apparatus within the vehicle concerned.
According to the invention, therefore, there is provided a rail vehicle for moving along a pair of parallel rails comprising a plurality of pairs of wheels arranged such that each one of each pair of wheels engages a respective one of the rails, at least one pair of the wheels being electrically interconnected so as to provide a short circuit across the rails and an apparatus for detecting the distance between the vehicle and a remote obstacle on the rails, the obstacle being of a type which varies the electrical conductivity across the rails, the apparatus including first contact means for engaging one of the rails at a position spaced from a respective wheel of said one pair of wheels, second contact means for engaging the other of the rails at a position spaced from the other wheel of said one pair of wheels, voltage generation means for applying a predetermined voltage difference between said first contact means and said one pair of wheels so as to generate a current in said one rail flowing from said first contact to said one pair of wheels and from said first contact along said one of said rails away from said one pair of wheels towards said obstacle, means for detecting the voltage difference between said second contact means and said one pair of wheels caused by current flowing from said obstacle to said one pair of wheels and means for displaying a signal generated in dependence upon the magnitude of said detected voltage difference so as to provide an indication of the distance between said vehicle and said obstacle.
The invention therefore uses the short circuit across the rails which is caused by the wheels of the next adjacent remote vehicle to generate a current from the first contact along the first rail to the short circuit back along the second rail to the second contact. The present inventor has realized that such a voltage can be applied to the rail despite the presence of a second short circuit across the rails provided by the next adjacent wheels of the vehicle on which the apparatus is positioned. The voltage applied at the first contact can be very low of the order of 0.1 volts which will avoid high currents in the rail portion between the first contact and the next adjacent wheels of the vehicle while generating a sufficient voltage at the second contact to provide a measurable voltage even over relatively long lengths of track between the vehicle and the remote vehicle.
Experiments show that detection of the next adjacent train can occur in good weather conditions at a distance of up to 100 miles.
The voltage can be applied to the rail by the first contact periodically and at a a frequency dependent upon the velocity of the vehicle. In cases where two such vehicles are equipped with the apparatus, the second vehicle can detect the pulses issued from the first vehicle and thus can measure its velocity in view of the known issued frequency.
With the foregoing in view, and other advantages as will become apparent to those skilled in the art to which this invention relates as this specification proceeds, the invention is herein described by reference to the accompanying drawings forming a part hereof, which includes a description of the best mode known to the applicant and of the preferred typical embodiment of the principles of the present invention, in which: